For the diagnosis of obstructive ventilation disorders, the lung function can be tested via the analysis of exhaled aerosol boll as described by T. Beinert et al in Pneumologie 44 (1990), Supplement 2, 1026. In this, one takes advantage of the fact that monodisperse inert aerosol particles with a given small diameter behave for the most part like a non-diffuse gas and can therefore be used as a marker for the convective gas transport. If such an aerosol is injected into the breathed air and inhaled as a low volume bolus, i.e. 20 cm.sup.3, then one can read the convective exchange of air volume between intrapulmonary residual air and inspired air via the volume in which the aerosol particles in the exhaled air are distributed. The shape and position of the exhaled bolus have changed with respect to the inhaled one. The measurement of the particle concentration as a function of the breathed volume is done via a continuously recording aerosol photometer and by using a monodisperse aerosol made of inert sebacic acid di(2-ethylhexyl) ester droplets (DEHS) for example.
The known measurement device consists of a valve block in which there is a breathing channel, an air channel and an aerosol channel. Inhalation and exhalation pass through the breathing channel, fresh air passes through the air channel and the aerosol passes through the aerosol channel. Control valves that control the supply of air and aerosol in the breathed air are part of the valve block. The control valves for air and aerosol are mechanical, electromagnetic or pneumatically operated so that during an inhalation phase the supply of fresh air is interrupted and can be replaced momentarily by the supply of aerosol. During this short switch over, an aerosol pulse is injected into the breathed air.
A typical breathing maneuver is shown in FIG. 8A; ascending curves correspond to the inspiratory phase E, descending curves to the expiratory phase A. During a deep inspiratory phase E.sub.t, a given air volume V.sub.i (i.e. 1 liter) is inhaled from FRC at a given volume flow (i.e. 250 cm.sup.3 /s). In this phase an aerosol bolus B.sub.i is injected into the breathed air and the aerosol is inhaled by the patient. An aerosol bolus B.sub.e appears in the exhaled air during the deep expiratory phase A.sub.t which follows the deep inspiratory phase.
The exhaled bolus B.sub.e is compared to the inhaled bolus B.sub.i for analysis as shown schematically in FIG. 8B. To characterize the dispersion, the positional shift and shape of the exhaled bolus is determined. The dispersion H is determined via a ratio of the half-width H.sub.50 of the inhaled and exhaled boll as per the equation EQU H=(H.sub.50e.sup.2 -H.sub.50i.sup.2).sup.1/2
The dispersion is a standard for the increase in volume in which the aerosol particles are distributed in the exhaled air. It describes the convective exchange between the intrapulmonary residual air and the inspired air. The positional shift M of the exhaled bolus is also determined with reference to the aerosol bolus in the inhaled air by the equation EQU M=V.sub.e -V.sub.i
One assumes a symmetrical concentration curve for the inhaled bolus. The asymmetry of the exhaled bolus is evaluated using shape deformation factors.
This example makes it clear how dependent therapy and diagnostics are on the quality of the aerosol pulse which is injected into the breathed air. Specifically the sharpness, i.e. the steepness of slope and the maximum achieved concentration of the aerosol pulse play a decisive role.